Pressure sensitive labels applied are applied to packages to build brand awareness, show the contents of the package, convey a quality message regarding the contents of a package, and supply consumer information such as directions on product use, or an ingredient listing of the contents. Prior art packaging labels are typically ink printed utilizing flexography or gravure cylinders. The three types of information applied to a pressure sensitive label are text, graphic, and images. Some packages only require one type of information, while other packages require more than one type of information.
Prior art labels that are applied to packages consist of a pragmatic sheet material, a pressure sensitive adhesive, and a carrier sheet. The label substrate consisting of the pragmatic sheet, pressure sensitive adhesive, and carrier sheet are typically laminated and then printed utilizing a variety of nonphotographic printing methods. After printing, the labels are generally protected by an over laminate material or a protective coating. The completed label consisting of a protection layer, printed information, pragmatic sheet, pressure sensitive adhesive, and carrier sheet material is applied to packages utilizing high speed labeling equipment.
Clear labels are currently utilized in packaging to provide a “no label look”. Typically, prior art clear labels comprise flexo printed ink on a transparent polymer substrate. The transparent polymer substrate, when applied to the package, allows the native color of the package and contents of the package to visually interact with the printed inks. Clear labels are also useful in allowing the consumer to observe the contents of the package when used in combination with clear packages such as clear water bottles and glass beverage bottles.
Flexography is an offset letterpress technique where the printing plates are made from rubber or photopolymers. The printing on pressure sensitive label is accomplished by the transfer of ink from the raised surface of the printing plate to the surface of the material being printed. The rotogravure method of printing uses a print cylinder with thousands of tiny cells which are below the surface of the printing cylinder. The ink is transferred from the cells when the print cylinder is brought into contact with the pressure sensitive label at the impression roll. Printing inks for flexography or rotogravure include solvent based inks, water based inks, and radiation cured inks. While rotogravure and flexography printing do provide acceptable image quality for most current applications, these two printing methods require expensive and time-consuming preparation of print cylinders or printing plates which make printing jobs of less than 100,000 units expensive. Setup cost and the cost of the cylinders or printing plates is typically depreciated over the size of the print job.
Recently, digital printing has become a viable method for the printing of information on packages. The term “digital printing” refers to the electronic digital characters or electronic digital images that can be printed by an electronic output device capable of translating digital information. The two main digital printing technologies are ink jet and electrophotography.
The introduction of piezo impulse drop-on-demand (DOD) and thermal DOD ink jet printers in the early 1980's provided ink jet printing systems. These early printers were very slow, and the ink jet nozzles often clogged. In the 1990's Hewlett Packard introduced the first monochrome ink jet printer, and, shortly thereafter the introduction of color, wide format ink jet printers enabled businesses to enter the graphic arts market. Today a number of different ink jet technologies are being used for packaging, desktop, industrial, commercial, photographic, and textile applications.
In piezo technology, a piezo crystal is electrically stimulated to create pressure waves, which eject ink from the ink chamber. The ink can be electrically charged and deflected in a potential field, allowing the different characters to be created. More recent developments have introduced DOD multiple jets that utilize conductive piezo ceramic material which, when charged, increases the pressure in the channel and forces a drop of ink from the end of the nozzle. This allows for very small droplets of ink to form and be delivered at high speed at very high resolution, approximately 1,000 dpi printing.
Until recently, the use of color pigments in jet inks was uncommon. However, this is changing rapidly. Submicron pigments were developed in Japan for ink jet applications. Use of pigments allows for more temperature resistant inks required for thermal ink jet printers and laminations. Pigmented water-based jet inks are commercially available, and UV-curable jet inks are in development. Pigmented inks have greater lightfastness and water-resistance.
Digital ink jet printing has the potential to revolutionize the printing industry by making short-run, color print jobs more economical. However, the next commercial stage will require significant improvements in ink jet technology; the major hurdle remaining is to improve print speed. Part of this problem is the limitation of the amount of data the printer can handle rapidly. The more complex the design, the slower the printing process. Right now they are about 10 times slower than comparable digital electrostatic printers.
Electrophotography was invented in the 1930's by Chester Carlson. By the early 1970's, the development of an electrophotographic color copier was being investigated by many companies. The technology for producing color copiers was already in place, but the market was not. It would take many more years until customer demand for color copies would create the necessary incentive to develop suitable electrostatic color copiers. By the late 1970's a few companies were using fax machines that could scan a document, reduce the images to electronic signals, send them out over the telephone wire and, using another fax machine, retrieve the electronic signals and print the original image using heat-sensitive papers to produce a printed copy.
In 1993 Indigo and Xeikon introduced commercial digital printing machines targeted on short-run markets that were dominated by sheet-fed lithographic printers. Elimination of intermediate steps associated with negatives and plates used in offset printing provides faster turnaround and better customer service. These digital presses share some of the characteristics of traditional xerography but use very specialized inks. Unlike inks for conventional photocopiers, these inks are made with very small particle size components in the range of 1 μm. Dry toners used in xerography are typically 8-10 μm in size.
In 1995 Indigo introduced the Ominus press designed for printing flexible packaging products. The Ominus uses a digital offset color process called One Shot Color that has six colors. A key improvement has been the use of a special white Electro ink for transparent substrates. The Ominus web-fed digital printing system allows printing of various substrates using an offset cylinder that transfers the color image to the substrate. In principle, this allows perfect register regardless of the substrate being printed, paper, film, and metal can be printed by this process. This digital printing system is based on an electrophotographic process where the electrostatic image is created on the surface of a photoconductor by first charging the photoconductor by charge corona and exposing the photoconductive surface to a light source in image fashion.
The charged electrostatic latent image is then developed using ink containing an opposite charge to that on the image. This part of the process is similar to that of electrostatic toners associated with photocopying machines. The latent charged electrostatic image formed on the photoconductor surface is developed by means of electrophoretic transfer of the liquid toner. This electrostatic toner image is then transferred to a hot blanket, which coalesces the toner and maintains it in a tacky state until it is transferred to the substrate, which cools the ink and produces a tack-free print.
Electro inks typically comprise mineral oil and volatile organic compounds. They are designed so that the thermoplastic resin will fuse at elevated temperatures. In the actual printing process, the resin coalesces and the inks are transferred to the substrate. There is no need to heat the ink to dry it. The ink is deposited on the substrate essentially dry, although it becomes tack-free as it cools and reaches room temperature.
For several decades a magnetic digital technology called “magnetography” has been under development. This process involves creating electrical images on a magnetic cylinder and using magnetic toners as inks to create the image. The potential advantage of this technology lies in its high press speed. Tests have shown speeds of 200 meters per minute. Although these magnetic digital printers are limited to black-and-white copy, developments of color magnetic inks would make this high-speed digital technology economically feasible. The key to its growth will be further development of the VHSM (very high speed magnetic) drum and the color magnetic inks.
Within the magnetic digital arena, a hybrid system called magnetolithography has been built and tested on narrow web and short-run applications developed by Nipson Printing Systems in Belfort, France. The technology appears to provide high resolution, and tests have been conducted using a silicon-based, high density, magnetographic head. Much more work is necessary in the ink development to bring this system to a competitive position relative to ink jet or electrophotography. However, the fact that it has high speed printing potential makes it an attractive alternate for packaging applications in which today's ink jet and electrophotography technologies are lagging.
Photographic materials have been known for use as prints for preserving memories for special events such as birthdays and vacations. They also have been utilized for large display materials utilized in advertising. These materials have been known as high quality products that are costly and somewhat delicate, as they would be easily defaced by abrasion, water, or bending. Photographs are traditionally placed in frames, photo albums, and behind protective materials in view of their fragile and delicate nature, as well as their value. They are considered luxury items for the consumers to preserve a record of important events in their lives. They also have been considered as expensive display materials for advertising. In view of their status as luxury items, they have not been utilized in other areas of commerce.
The use of a clear substrate in a photographic material can present many problems. Scratch resistance of the photographic emulsion is an important consideration. Optical degradation due to light wave reflection off the backing material is an important problem to solve. Optical interference during printing and during densitometric evaluation is another problem to solve. In some applications, this opaque printing may be desirable on a clear label to set the text off from the product inside. An example of this may be a product with an abundance of texture, such as peanuts or candy. Providing a combination of opacity and transparency with a photographic media requires a novel approach.
Typically pressure sensitive labels are supplied with a carrier sheet web material that allows the pressure sensitive label to be transported though the printing process and converting process while protecting the adhesive. Prior art carrier sheet materials typically comprise a coated paper or a thin polymer carrier sheet onto which a release coating is subsequently provided. Carrier sheet materials typically utilized in the pressure sensitive label are not suitable for a photographic label. Problems such as photographic reactivity with the light sensitive layers, lack of stiffness of the carrier sheet, and edge penetration of processing chemistry into the paper used as a carrier sheet prevent typical polymer and paper carrier sheets from being utilized for photographic pressure sensitive labels. Further, in U.S. Pat. No. 5,866,282 (Bourdelais et al), the need for a white reflecting layer under the emulsion for a high quality silver halide image formulation is proposed. Printing a silver halide image without a white reflecting layer will result in a loss of printing speed, image sharpness and poor quality test.